Researchers found that Bifidobacterium animalis produced mannose, activated tumor-fighting CD8+ T cells and improved the effectiveness of anti-PD-1 immunotherapy in laboratory and mouse experiments.
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A probiotic bacterium commonly found in yogurt and dietary supplements may help the immune system fight melanoma by producing a natural sugar that enhances anti-tumor activity, according to a study published in a peer-reviewed journal.
Researchers reported that Bifidobacterium animalis produces mannose, which appeared to strengthen the ability of immune cells to enter tumors and slow their growth.
The findings were based on laboratory cell cultures and experiments involving mice with melanoma. The research did not test the treatment in people, and investigators cautioned that neither B. animalis nor mannose should be used as a cancer therapy based on the current evidence.
The study adds to research examining how the gut microbiome influences immune function and the body’s response to cancer.
According to the researchers, the observed anti-tumor effect depended on CD8+ T cells, immune cells that recognize and attack abnormal cells, including cancer cells.
Researchers Test Bacterium in Melanoma Models
The team conducted experiments in laboratory cultures and mouse models to determine whether B. animalis influenced melanoma growth through the immune system.
Mice with melanoma tumors received the bacterium orally. Tumors grew more slowly in those animals than in the control groups, according to the study.
Researchers also found that more CD8+ T cells entered the tumors after the mice received B. animalis.
To determine whether those immune cells were responsible for the effect, the researchers removed CD8+ T cells from a separate group of mice. Once the cells were removed, the bacterium no longer slowed tumor growth.
That result indicated that the anti-tumor benefit required CD8+ T-cell activity rather than a direct attack by the bacterium on melanoma cells.
The experiments were designed to separate immune-mediated effects from any possible direct interaction between B. animalis and cancer cells.
The research builds on earlier studies indicating that probiotic bacteria can influence immune responses.
A study published in the Journal of Nutrition found that honey helped B. animalis survive in the digestive tract, suggesting that dietary factors may influence the bacterium’s ability to remain active.
Other researchers have examined the immunostimulatory properties of gut bacteria in relation to cancer treatment, including the use of fecal microbial transplantation to improve responses to immune checkpoint inhibitors among patients with advanced melanoma.
Mannose Identified as Key Compound
The researchers traced the bacterium’s effect to mannose, a naturally occurring sugar produced by B. animalis.
According to the study, mannose inhibited a protein called YAP1 inside immune cells.
YAP1 normally helps suppress immune activity. When mannose inhibited the protein, the CD8+ T cells became more active and better able to perform their anti-tumor functions, the researchers reported.
With YAP1 blocked, the immune cells operated at greater capacity and were more effective at targeting melanoma tumors.
The study also found that mannose selectively increased levels of certain beneficial intestinal bacteria, including B. animalis, without broadly disrupting the rest of the gut microbial community.
Researchers said that selective effect could help maintain an intestinal environment that supports continued immune activity against tumors.
The findings are consistent with the broader understanding of the gut-immune axis.
The gastrointestinal tract contains large numbers of immune cells, and substances produced by commensal bacteria can influence inflammation, immune signaling and the body’s defenses against disease.
Previous studies have also found that certain Bifidobacterium strains can produce anti-inflammatory effects through signaling pathways in intestinal cells.
Combination Improves Immunotherapy Response in Mice
The study also examined whether B. animalis could improve the effectiveness of anti-PD-1 therapy, a widely used form of cancer immunotherapy.
Anti-PD-1 drugs work by blocking a molecular checkpoint that cancer can exploit to suppress T-cell activity. Removing that restraint can allow immune cells to recognize and attack tumors more effectively.
When researchers combined B. animalis with anti-PD-1 treatment, the combination slowed melanoma growth more effectively than either intervention alone, according to the study.
Mannose produced a similar effect when administered with anti-PD-1 therapy.
The researchers said the results suggest that the bacterium or its mannose production could potentially complement checkpoint immunotherapy.
More than half of patients treated with anti-PD-1 therapy eventually stop responding, the researchers noted. The findings therefore raise the possibility of developing a strategy to strengthen or extend treatment responses.
That possibility remains unproven in humans.
Researchers emphasized that clinical trials would be required to determine whether B. animalis, mannose or a related treatment could safely improve immunotherapy outcomes in cancer patients.
Probiotics have previously been associated with immune support in other settings. Certain strains have been linked to stronger immune responses against colds and influenza and to reductions in illness severity.
Other research has suggested that probiotics may strengthen immune defenses and help protect against some infections.
The current study extends those observations into cancer immunotherapy, but the experimental results cannot yet be translated into treatment recommendations.
Human Benefits Remain Uncertain
The investigators stressed that the research remains preclinical because it relied on laboratory cultures and mice rather than human participants.
“These findings are early-stage and require validation in human trials,” the researchers stated.
Biological responses observed in mice do not always occur in humans. Researchers would also need to establish an appropriate dose, method of delivery, treatment duration and safety profile before any clinical use could be considered.
Commercial probiotic products can vary considerably in bacterial strain, concentration, purity and viability. A yogurt or supplement containing B. animalis would not necessarily reproduce the conditions or results of the study.
Experts therefore cautioned against taking B. animalis or mannose supplements to prevent or treat melanoma.
No specific probiotic product can currently be recommended as a cancer therapy, according to the researchers.
The study nevertheless contributes to growing evidence that intestinal microbes and the substances they produce can affect immune function beyond the digestive tract.
Further research could determine whether the bacterium’s effects can be replicated in people and whether mannose or related compounds can be developed into controlled treatments that support existing immunotherapies.
Maintaining a healthy gut microbiome through diet and lifestyle may support general immune health, the researchers noted, but it should not replace standard cancer screening, medical evaluation or treatment.
For now, the findings identify B. animalis and mannose as promising subjects for further investigation rather than established tools for melanoma care.
Source: Natural News
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